Mobile terminals, such as mobile phones or personal digital assistants (PDAs), are, by nature, driven by a rechargeable battery, and in order to charge the battery, electric energy is supplied to the battery of the mobile terminal by using a separate charger. Typically, the battery and the charger are provided with separate contact ports on the outer surface thereof so that the contact ports come into contact with each other in order to electrically connect the charger with the battery.
However, since the contact ports protrude from the outer surface in the contact charging type, the contact ports tend to be easily contaminated with foreign substances, which may bring about a failure of the battery charging operation. In addition, exposing the contact ports to moisture disrupts the charging operation.
In order to solve the problems above, in recent years, wireless charging or contactless charging technology has been developed to be utilized in various electronic devices.
The wireless charging technology uses a wireless power transmission/reception system. For example, when a mobile phone is placed on a charging pad without being connected to a separate charging connector, the battery is able to be automatically charged. In general, the wireless charging technology is used for a cordless electric toothbrush or a cordless electric shaver, both of which are well known devices. Since the electronic devices are wirelessly charged according to the wireless charging technology, a waterproof function thereof may be enhanced. In addition, the portability of the electronic devices may be improved because a wired charger is not necessary. Wireless charging-related technology is expected to grow significantly in the coming electric vehicle era.
Wireless charging technology may be divided into an electromagnetic induction type using coils, a resonance type using resonances, and a radio frequency (RF)/micro-wave radiation type that converts electric energy into microwaves which are then transmitted.
Although the electromagnetic induction type has been widely used until now, they have recently succeeded in an experiment in which power is wirelessly transmitted tens of meters by using microwaves at home and abroad. Therefore, it is expected that all electronic devices may be wirelessly charged without cables, anytime and anywhere, in the near future.
Power transmission by electromagnetic induction may be made by power transmission between a primary coil and a secondary coil. According to the phenomenon in which a moving magnet near the coils generates an induction current, the magnetic field may be generated at a transmitting end, and a current may be induced due to a change in the magnetic field at a receiving end in order to thereby generate energy. This phenomenon is called magnetic induction, and power transmission using magnetic induction is excellent in energy transmission efficiency.
With regard to the resonance type, in 2005, Marin Solja{hacek over (c)}ić, a professor in the Massachusetts Institute of Technology (MIT), announced a system in which power is wirelessly transmitted from a charger to an electronic device that is several meters away by using a resonant power transmission method with coupled mode theory. The wireless charging system of an MIT team uses the physical concept of a resonance, such as when a wine glass near a vibrating tuning fork oscillates in the same frequency as the tuning fork. The team has used electromagnetic waves containing electrical energy instead of sounds. Since the resonated electrical energy is directly transferred only when there is a device having the resonance frequency, and the unused portion thereof is re-absorbed into the electromagnetic field without spreading into the air, it is expected to not affect neighboring machines or a human body unlike other electromagnetic waves.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.